1. Field of the Invention
The present invention relates to systems and methods for transmitting and receiving data, and in particular to a system and method for transmitting and receiving data with lower complexity equipment.
2. Description of the Related Art
Digital signal communication systems have been used in various fields, including digital TV signal transmission, either terrestrial or satellite. As digital signal communication systems and services evolve, there is a burgeoning demand for increased data throughput and added services. However, it is more difficult to implement either improvement in old systems or new services when it is necessary to replace existing legacy hardware, such as transmitters and receivers. New systems and services are at an advantage when they can utilize existing legacy hardware. In the realm of wireless communications, this principle is further highlighted by the limited availability of electromagnetic spectrum. Thus, it is not possible (or at least not practical) to merely transmit enhanced or additional data at a new frequency.
The conventional method of increasing spectral capacity is to move to a higher-order modulation, such as from quadrature phase shift keying (QPSK) to eight phase shift keying (8PSK) or sixteen quadrature amplitude modulation (16QAM). Unfortunately, QPSK receivers cannot demodulate conventional 8PSK or 16QAM signals. As a result, legacy customers with QPSK receivers must upgrade their receivers in order to continue to receive any signals transmitted utilizing 8PSK or 16QAM modulation.
It is advantageous for systems and methods of transmitting signals to accommodate enhanced and increased data throughput without requiring additional frequency. It is also advantageous for enhanced and increased throughput signals for new receivers to be backwards compatible with legacy receivers. There is further advantage for systems and methods which allow transmission signals to be upgraded from a source separate from the legacy transmitter.
It has been proposed that a layered modulation signal, transmitting non-coherently upper as well as lower layer signals, be employed to meet these needs. Such layered modulation systems allow higher information throughput with backwards compatibility. However, even when backward compatibility is not required (such as with an entirely new system), layered modulation can still be advantageous because it requires a TWTA peak power significantly lower than that for conventional 8PSK or 16QAM modulation formats for a given throughput.
However, a significant roadblock associated with implementing a layered modulation is the requirement for the use of a separate forward error correction (FEC) routine and implementing circuitry for each layer. This requirement increases the complexity of the associated transmission and reception systems and also increases the overall cost. What is needed is a system and method for transmitting and receiving such signals without need for multiple encoders/decoders. The present invention satisfies this need.